This invention relates generally to a hand-operated pneumatic power tool having improved means for attenuation of both vibration and noise when being operated and more particularly to the construction of such type tool device which employs a reciprocating work member such as a chisel, hammer or the like.
Various means are already known to nullify or reduce considerable impact otherwise experienced by operators of pneumatic power tools, both hand-held and hand-operated, to include chippers, hammers, tampers, jack hammers and the like. In addition to requiring considerable strength to operate such tools, the continuous comparatively large amplitude impacting mechanical forces associated with the recoil reaction of the reciprocating work member often results in serious physical harm to the tool operator. Thus, there has long been a need for vibration attenuation in such pneumatic powered impact tools so that little if any cyclical impact forces will be transmitted to the tool operator. Likewise, various federal and state governmental agencies are becoming increasingly concerned with the serious need to reduce noise in the work place based on either health considerations for the work force or disturbance to the surrounding population.
Pneumatic dampening of the reciprocating work member has been employed as a known means to secure vibration attenuation for a variety of such impact tools. For example, such pneumatic attenuation means are disclosed in U.S. Pat. No. 3,456,744 whereby the recoil of a free piston member in such type device is dampened with a pneumatic counterforce. As therein described at the time the piston starts backward movement there is gas pressure between the forward face of the piston and the tool member tending to drive the piston backward. The volume between the rear of the piston and the closed end of a movable sleeve member is vented to the atmosphere. As the piston moves backward the movable sleeve member moves forward under gas pressure in a peripherally located chamber between said sleeve member and a further tool member in the device and between the forward face of the piston and the sleeve member. As the sleeve member moves forward, the passage is closed thereby trapping gas between the rear face of the piston and the closed end of the sleeve member. Also, the volume between the piston and tool bit is closed thereby retaining the gas therein which expands as the piston moves to the rear. Compression of the gas in the volume between the rear Face of the piston and the closed end of the sleeve member tends to decelerate both the piston and the sleeve member without imparting cyclic recoil forces to the tool member, barrel member or the handle in said device. A similar vibration dampening mechanism is described in U.S. Pat. No. 4,398,411 wherein the vibration and recoil otherwise experienced during operation of a rivet bucking tool is absorbed in the tool housing with compressed air being introduced into a dampening chamber. The pressure of the reduced air from an outside source is made adjustable with valve means while a further O ring element in this tool construction is also reported to resiliently dampen forward impact by the reciprocating piston.
Still other type deformable attenuation means have been utilized in pneumatic impact tools to minimize vibration, including employment of elastomeric buffers and mechanical springs. For example, a hand-held pneumatic powered tool of this type is disclosed in U.S. Pat. No. 5,054,562 which is constructed of rigid parts isolated from each other by elastomeric shock-absorbing material arranged between the parts in laminar fashion in which certain of the layers are of a different Shore A hardness as respect each other. The layers are reported to be formed with different thicknesses which are introduced into an annular space between the parts in pourable condition, each layer being permitted to set-up before the next layer is poured, which results in bonding of the elastomeric layers to each other as well as to the parts. A novel supporting structure is reported to be disposed between the parts to space them in condition to receive the elastomeric material and the structure is permitted to remain between the parts in such isolated or shock-absorbing fashion so as to improve the vibration-minimizing characteristics of the overall construction. Elastomers reported to be useful for such device construction are any of the known liquid polyurethane types pourable at room temperature or up to about 100.degree. F. and with decreasing Shore A hardness being exhibited in successive layers of the poured elastomer. In U.S. Pat. No. 5,407,018 there is also disclosed elastomeric attenuation means having a novel multi-part construction for impact tools to provide a still greater degree of vibration and noise attenuation. A still different vibration and noise
attenuation construction for impact tools which employs oppositely biased metal springs is similarly disclosed in U.S. Pat. No. 4,359,225.
It is an object of the present invention, therefore, to provide still further improved means for vibration and noise attenuation in a pneumatic impact tool requiring only a relatively simple modification of the existing tool construction.
A still further object of the present invention is to provide the desired improvement in a distinctive manner involving cooperation between component parts of a multi-part attenuation means.
It is yet another object of the present invention to provide the desired improvement in a variety of pneumatic powered impact tools including the type employing a replaceable reciprocating impact member.
These and still further objects of the present invention will become apparent upon considering the following detailed description of the present invention.